This invention relates to an apparatus for sorting chip-like or wafer-like material by length, and relates particularly to an apparatus suitable for use in sorting jumbo wood chips or wafers by length.
In many wood utilizing processes, it is common to reduce pulp wood logs into chips before further processing. To utilize the chips, it is preferred that from each individual chip to another certain physical characteristics do not vary substantially. In some processes, chip thickness has been perceived as a critical characteristic which should not vary significantly from chip to chip. For example, in the papermaking process, wood chips are cooked in digesters with chemicals at elevated temperatures and pressures to remove lignin and to liberate individual fibers. To prevent underprocessing or overprocessing of individual chips, liquor absorption must be consistent from chip to chip. Thus, it is desirable that all chips be within a specified chip thickness range, to promote consistent processing, and that thinner or thicker chips be processed independently from the main volume of chips falling within the accepted size range.
Various screening and sorting apparatus have been used for sorting chips by chip thickness. Particularly efficient and advantageous processes have been designed including the use of disk screens, in which a plurality of disks are located on a shaft and are positioned adjacent other shafts having disks, with the disks of one shaft interdigitating with the disks of the adjacent shaft. Spacing between adjacent interdigitated disks is uniform. Operation of the screen orients the chips to present the chip thickness dimension to the spaces between interdigitated disks. In this manner, disk screens have been used effectively and efficiently for sorting chips by thickness. In thickness screens, chip length is not measured, and chips of various lengths but similar thickness are processed together.
In other chip utilizing processes, however, it is important to sort the chips by chip length. For example, in manufacturing wafer board, while chip thickness is important, chip length is also a significant physical characteristic. It is often preferred that only chips of a specified minimum chip length be used. Length is particularly important when jumbo wafers are utilized; that is, wafers which may be several inches to one foot in length. Sorting such chips by length has been difficult in the past, and no suitable device for sorting by length in a continuous process has been available. A suitable device for sorting such chips by length must operate to measure the length of the chip, regardless of how the chip is presented to the screening device; and a suitable apparatus must insure that the length dimension used for separation, not the width or thickness dimension. The device should operate to sort a continuous flow of chips efficiently at high volume and with minimal or no plugging.
Shaker screens have been used for screening chips by length with unsatisfactory results, particularly when jumbo wafers are processed. Processing capacities are low, and chips longer then the designed separation length may pass through the screen if the chip is tipped or tilted with respect to the screen openings. Particularly with regard to jumbo wafers wedging in the openings may cause blinding of the screen, further reducing screen capacity and efficiency.